1. Field of the Invention
The present invention relates to flexible electrical connectors that are permanently bonded onto contact pads of semiconductor devices and to a method of making stabilized closed configuration connectors with an automatic wedge wire bonder. More particularly, the present invention provides a reworkable flexible connection that may be configured to different shapes when bonded to electrical contact pads of a semiconductor device using only one bonding step.
2. Description of the Prior Art
Most semiconductor devices are provided with lead-out pads or electrical contact pads which are intended to be connected to packages, lead frames, circuit boards, substrates and various forms of carriers. It is well known in the semiconductor packaging art that the coefficient of thermal expansion of the semiconductor device is seldom if ever matched to the carrier or the substrate to which it is to be attached. To compensate for this difference in thermal expansion and to avoid breaks in connections and disconnections which often occur after passing testing operations, it has been common practice to use flexible conductive connectors which extend outward and downward from the semiconductor device. Semiconductor devices that are wire bonded to a substrate, lead frame, or carriers with flexible wire connections are almost impossible to rework should one of the many wire bond connections prove to be faulty after the semiconductor device is wire bonded.
Some high density semiconductor die are provided with solder or gold bumps instead of the usual square or rectangular bonding pads. Devices in this category usually fall into a category of Ball Grid Array (BGA) and/or Direct Chip Attach (DCA) flip-chip devices so named because the device is placed balls down on the substrate or carrier that has a connection pattern matching the array of bumps or balls. A series of steps are needed and employed to make bumps or to place balls in sockets to complete BGA connections on the flip-chip semiconductor device or BGA devices. The same problems that exist with all flip-chip type devices still exist. That is, BGA and flip-chip devices are prone to failure because of the differential thermal expansion between the semiconductor device and the substrate or carrier to which it is connected. Further, should the semiconductor device or any one ball or bump connector fail after integration into or onto a circuit board, it is not feasible to salvage the device or the circuit board.
The unsolved prior art problems are well described in U.S. Pat. No. 6,049,976, which is incorporated herein by reference and includes the many prior art references cited in the patent. Most of the references are found in class 29/subclasses 842–844 et seq. and class 228/subclasses 45 et seq. enumerated in the field of search. Basically the U.S. Pat. No. 6,049,976 teaches a stem of bonded wire which is plated and/or coated to form protrusions or connectors. Two forms of protrusions are described; one form is a spring and the other form a more rigid bump shape. The protrusions are made from layers of a metallic conductive material deposited or plated on free standing stems to provide a resilient or rigid protrusion. At least one embodiment teaches making tower like solder contacts (bumps) which define a final rigid shape even after multiple reflow steps.
Every stem or protrusion involves one or more process steps which follow the step of the bonding of the wire to produce an initial contact. The final spring like contact is moveable in a vertical and X-Y plane and cannot be reworked after being permanently soldered to a substrate or carrier.
An excellent summary of the problems associated with flip-chip packaging is found in the July 2001 issue of Advance Packaging at pages 67–71.
The present invention provides a novel solution to the decades old problem of the prior art in that the present invention resilient contacts can be made in one wire bonding step without subsequent processing steps and when rework is required the die, chip or device can be removed, repaired and reused as will explained in greater detail hereinafter.
It is highly desirable to provide a wire bonded chip or interposer which has all of the advantages of flip-chip devices and BGA devices and yet has none of the disadvantages described in the prior art patents and publications mentioned above.